Process For Separating Used Oil

ABSTRACT

A process for removing impurities from used oil. Impurities such as water, solid particles, and the like are removed from used oil by processing the oil with a mixture of polar and non-polar solvents. The process operates at room temperatures and pressures, simplifying the equipment and energy requirement for the process.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates to used oil. More specifically, the present invention relates to a process for separating impurities from used oil and for making the used oil suitable for use as a base material in making fuels or lubricants.

2. State of the Art

Currently, a large amount of used oil is produced world wide. The used oil may be from many sources, a common source being engine lubricants. Millions of gallons of used lubricant oil is generated annually from motor vehicles and from industrial users. The large number of automobiles, trucks, trains, boats, etc. which are used for transportation, and the regularity with which the engine lubrication should be changed, result in a large amount of used motor oils. It can easily be appreciated that a significant amount of used oils are generated.

In some instances, used oils have simply been discarded. Some attempts have been made to create products which absorb and hold the oil, allowing a person to drain motor oil or the like into a container and then simply discard the container of oil. Discarded oil poses an environmental hazard as it can pollute the soil and groundwater. In many instances, pollutants in the soil and groundwater migrates into waterways and results in pollutes drinking water. It can easily be understood that simply discarding used oils is not the most desirable alternative, especially when considering the demand for petroleum and the environmental risks associated with disposing the oil in a landfill.

Further attempts have been made to find alternate uses for used oils, thus providing a more economically viable and environmentally friendly method of disposing of the oils. For example, used oils have been filtered and used as a low grade burner fuel. While better than simply disposing of the oil, it would be desirable to use the oil for a more economically valuable purpose.

In finding ways to process used oil and create a marketable product, several obstacles must be overcome. One obstacle is the composition of the used oil itself. Used oil is a complex substance, containing the lubricant oil, value added components such as additives, and undesirable compounds including heavy metals and toxic compounds. Used oils will typically contain metals, carbon particles, lubricant additives, water, antifreeze, etc. In some used motor oil collection sites, the used oil may be collected with transmission fluids, gear lubricants, antifreeze, etc. Thus, the used oil collected is a mixture containing many impurities and additives or modifiers. These components make it difficult to process or refine the used oil.

A further difficulty in processing used oil is that the overall process must be economical. If the process for separating and purifying the used oil is too expensive, it will result in a product which can not be sold. A process for purifying used oil should cost less than the purified oil is worth afterwards.

There is thus a need for an economical method for separating used oil which removes the impurities and undesired components from the used oil. There is a need for an economical process for separating a high quality oil base stock from the used oil.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved method for separating used oil in to impurities and usable components.

The invention utilizes a mixture of polar and non-polar solvents to separate the impurities from the used oil. After separating the impurities, the solvent mixture is separated from the oil and is reused. The ability to reuse the solvent mixture allows the process to be economically viable and environmentally friendly.

The invention allows for the processing of the used oil at low temperatures and pressures, reducing the equipment complexity and reducing the energy requirements for the process.

These and other aspects of the present invention are realized in a process for separating used oil as shown and described in the following figures and related description.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention are shown and described in reference to the numbered drawings wherein:

FIG. 1 shows a schematic diagram of a process of the present invention;

FIG. 2 shows a process diagram of the present invention;

FIG. 3 shows a process diagram of the present invention;

FIG. 4 shows another schematic diagram of the present invention; and

FIG. 5 shows another process diagram of the present invention.

It will be appreciated that the drawings are illustrative and not limiting of the scope of the invention which is defined by the appended claims. The embodiments shown accomplish various aspects and objects of the invention. It is appreciated that it is not possible to clearly show each element and aspect of the invention in a single figure, and as such, multiple figures are presented to separately illustrate the various details of the invention in greater clarity. Similarly, not every embodiment need accomplish all advantages of the present invention.

DETAILED DESCRIPTION

The invention and accompanying drawings will now be discussed in reference to the numerals provided therein so as to enable one skilled in the art to practice the present invention. The drawings and descriptions are exemplary of various aspects of the invention and are not intended to narrow the scope of the appended claims.

Generally, the invention uses a mixture of chemicals to separate impurities from used oil. Table 1 illustrates exemplary chemicals as may be used in the present invention.

TABLE 1 Dielectric Boiling Constant Dipole Point Density (g/cc Chemical: at 25° C. Moment O/C ratio (° C.) at 20° C.) MEK 18.5 2.5 0.25 79.6 0.805 Acetone 20.7 2.88 0.33 56.2 0.790 Pentane 1.84 0.0 0 36.1 0.626 Hexane 1.89 0.08 0 69.0 0.660 Cyclohexane 2.02 0.0 0 80.7 0.778

The process described herein utilizes the properties of different solvents to separate the impurities from the used oil. Table 1 illustrates both polar and non-polar solvents. It can be seen that the polar solvents such as methyl ethyl ketone and acetone typically have some similar characteristics such as a high dielectric constant, dipole moment, and oxygen to carbon (O/C) ratio. Similarly, the non-polar solvents such as pentane, hexane, and cyclohexane typically have low dielectric constants, dipole moments, and O/C ratios. For convenience, the solvents will be referred to herein simply as polar and non-polar solvents.

The present invention utilizes a mixture of a polar solvent and a non-polar solvent to separate the impurities from used oil. Without the use of solvents, the impurities in the used oil are difficult to separate from the used oil. The use of a polar/non-polar solvent mixture allows the impurities to be easily separated from the oil by gravity, filtration, etc.

While not intended to be limiting of the present invention, it is believed that the solvent mixture used in the present invention both promotes some flocculation or clumping of the impurities in addition to disturbing the equilibrium that tends to hold the impurities in suspension in the used oil.

Used oil can vary greatly in composition, and may often contain between 20% and 40% oil, 10% to 40% additives, 10% to 15% water, and 15% to 60% impurities. Used lubricant oil may often be collected together with used transmission fluid, hydraulic fluid, antifreeze, etc. Thus, the used oil may differ considerably for different collection locations or even for different times of collection from a particular location. The inventive process is advantageous as it can be used to process many different types of used oil without significant modification.

Turning now to FIG. 1, a basic schematic diagram of a process for separating used oil 10 according to the present invention is shown. One of the samples of used oil 10 which was separated with the present invention was tested and was determined to include approximately 40.7% oil, 32.5% additives (such as the additives used in creating motor oil) 11.5% water, and 15.3% impurities. The impurities were solids, and included particulate carbon as well as metals. An analysis of the impurities revealed that the metal content of the used oil impurities was 11.5 ppm barium, 31.2 ppm copper, 9.8 ppm lead, 48.4 ppm molybdenum, 3.5 ppm vanadium, 424.0 ppm zinc, 1410.0 ppm calcium, and 4.7 ppm manganese. As discussed herein, impurities refers to the solids present in the used oil.

The used oil 10 is mixed with a solvent mixture 14. The solvent mixture 14 is a mixture of a polar and a non-polar solvent. It has been determined that the preferred mixture of solvents is about 5 to 15 percent non-polar solvent by volume, with the remaining 85 to 95 percent being polar solvent. It is believed that the solvent mixture will work with between 2 and 25 percent non-polar solvent and the remaining 75 to 98 percent being polar solvent, but it is currently preferred to have between 5 and 15 percent non-polar solvent in the solvent mixture, and more preferred to have about 10 percent non-polar solvent. Although somewhat higher or lower percentages of non-polar solvent in the solvent mixture 14 will work, the above ratio has been found to be more effective, with 10 percent non-polar solvent being particularly desirable. In many cases, pure polar solvent or a mixture with little non-polar solvent will not mix well with the used oil. Similarly, pure non-polar solvent or too much non-polar solvent in the solvent mixture 14 will mix well with the used oil, but will tend to keep the impurities suspended in the liquid rather that separating the impurities from the oil.

An important discovery of the present invention is that the above mixtures of non-polar solvent and polar solvent will be fully miscible with the used oil, and will also cause the impurities to separate from the resulting solution and therefore be easily removable from the solution. It has been discovered that 100 percent polar solvents will not mix well with the oil, and that 100 percent non-polar solvents will not effectively separate the impurities from the used oil.

According to the present invention, ketones are the preferred polar solvents. Acetone is the preferred ketone, as it has a good polarity and power as a solvent, and also has a reduced boiling point which allows for reduced temperatures when removing the solvents from the oil. Aliphatic solvents are the preferred non-polar solvents, with hexane being the preferred chemical. Hexane is effective in making the acetone miscible with the used oil, allows the impurities to separate from the used oil, and has a reduced boiling point comparable with the acetone.

In achieving an appropriate mixture of solvents, other solvents such as toluene or acetonitrile were used. Toluene and acetonitrile were not highly effective in separating the impurities from the used oil 10. Other ketones and aliphatic solvents are expected to work. A disadvantage of using other ketones or aliphatic solvents is that these will typically have higher boiling points than acetone and hexane. An undesirably high boiling point results in a high temperature when separating the solvent from the used oil. Overly high temperatures may encourage further cracking or degradation of the used oil 10.

The used oil 10 and solvent mixture 14 are mixed in a vessel 18 in a desired ratio. Typically, about 15 to 50 percent used oil 10 and about 50 to 85 percent solvent mixture 14 is used. Thus, the resulting mixture of used oil 10 and solvent mixture 14 may typically contain between 2 and 13 percent non-polar solvent, between 42 and 81 percent polar solvent, and between 15 and 50 percent used oil.

The mixing of the used oil 10 and the solvent mixture 14 causes the impurities to separate from the used oil and settle out as sediment rather than being held in suspension. Thus, in a vessel 18, a liquid phase 22 having solvent mixture 14 and used oil 10 (less impurities) and a sediment phase 26 having largely impurities with some solvent mixture and used oil are formed. The sediment phase 26 is collected into a container 30 and the liquid phase 22 is collected into another container 34.

Turning now to FIG. 2, a process diagram for separating used oil according to the present invention is shown. FIG. 2 illustrates the basic process of FIG. 1 and includes additional processes necessary for economic viability of the process, such as recycling of the solvent mixture 14. Common system elements such as pumps are not shown, but are understood to be necessary and are within one of skill in the art. As such, the above discussion of the invention also applies to FIG. 2.

The used oil 10 and solvent mixture 14 are mixed together. A mixer 38 may be used if desired to mix the used oil and solvents. The used oil 10 and solvent mixture 14 are then introduced into a vessel 18. Slow mixing of the contents of the vessel 18 may be achieved by a mixer 40 to speed up the liberation of the impurities from the used oil. If the impurities are separated from the oil and solvent by a settling process, the mixer 40 would operate at a slow speed to not impede the settling process. A sediment layer 26 and liquid layer 22 are formed. The liquid in the vessel 18 including the liquid layer 22 includes processed oil (used oil having the solid impurities separated therefrom), additives, water, and solvent mixture 14. Because of the volume of solvents necessary for processing the used oil 10, it is desirable to recover the solvents. Thus, the liquid layer 22 may be passed to a distillation column 46. The distillation column 46 may be used to separate the oil and additives 34, water 54, and solvent mixture 14.

It will be appreciated that the polar solvent used in the solvent mixture 14 will absorb the water from the used oil. If the water is not removed from the solvent mixture, the solvent mixture 14 will become diluted and lose the ability to separate the impurities from the used oil. The oil and additives 34, water 54, and solvent mixture 14 may be separated in the various stages of a single distillation column, or may be separated in two distillation columns if desired.

The sediment layer 26 may be withdrawn from the vessel 18. As the sediment layer 26 will contain some liquid (oil and solvent mixture), it may be desirable to pass the sediment layer 26 through a filter 42 to separate the impurities 30 from the liquid 62 contained therein (which is the same as the liquid 22). The liquid 62 may be combined with the liquid layer 22 to separate the oil and additives 34, water 54, and solvent mixture 14.

As solvents such as acetone and hexane are more expensive than oil or gasoline, it is important to recover and recycle the solvents to achieve an economically feasible operation. Thus, the amount of solvent mixture 14 remaining in the impurities 30 and the oil and additives 34 should be minimized. Additionally, the amount of the solvent mixture 14 lost in the water 54 should be minimized. As the solvent mixture 14 will still function with some water contained therein, it may be more important to leave some water in the recycled solvent mixture than to lose some solvent mixture in the water 54.

FIG. 3 shows an alternate equipment configuration for according to the used oil separation of the present invention. The process is similar to that of FIG. 2, with the primary difference being that the vessel 18 has been eliminated and the entire mixture of used oil 10 and solvent mixture 14 are passed through the filter 42. The filter will separate the impurities 30 from the liquid stream 66 which includes the oil, additives, water, and solvents. The liquid stream 66 is then passed to the distillation column 46 and separated as discussed.

For the used oil tested, the impurities separated from the oil were about 15.3 percent of the used oil by weight, and contained solid carbon and metals as described above. Prior to processing, the used oil was dark brown and opaque in appearance, likely due to the carbon particles in the oil. After processing according to the above methods, the recovered oil consisted of the oil and additives, and was a lighter brown color and was transparent.

One advantage of the methods discussed above for separating impurities from used oil is the ability to perform the same without requiring elevated temperatures and pressures. If acetone and hexane are used as the polar and non-polar solvents, the mixture of solvent mixture 14 will effectively separate the impurities from the used oil 10 at room temperature and pressure. It is appreciated that processes requiring elevated temperatures are generally more difficult and costly to construct and operate, while system which can operate at atmospheric pressure and lower temperatures are simpler to construct and operate. These systems require less complex equipment, and may use a simple heating source such as steam.

Acetone has a boiling point of about 55 degrees centigrade and hexane has a boiling point of about 65 degrees centigrade. Thus, the distillation of a mixture of these solvents and oil mixture may be achieved using steam or heated water as a heat source, and the condensed solvents will typically be at a temperature of about 60 degrees centigrade or lower, and may be directly recycled into the system. It is believed that a slight elevation of temperature, such as may be achieved by recycling the condensed solvents, may add to the speed or efficiency of separating the impurities from the used oil. In such a situation, the mixture of used oil and solvents may have a temperature of about 40 degrees centigrade. Preventing heat loss from the condensed solvents and preventing heat loss from the system in general may reduce the amount of energy required to distill the processed oil and solvent mixture to separate the oil, water, and solvent mixture.

Turning now to FIG. 4, another basic schematic diagram of the inventive process of the above figures is shown. The used oil 10 is mixed with a solvent mixture 14. As discussed above, the solvent mixture 14 is a mixture of polar solvents and relatively non-polar solvents. It will be appreciated that, while discussed herein as a mixture of a single polar solvent and a single non-polar solvent, the present invention may function equally well using two or more polar solvents or non-polar solvents. A mixture of hexane and pentane may be used, for example, to adjust the boiling point of the solvent mixture.

An important discovery of the present invention is that the solvent mixture 14 is fully miscible with the used oil 10, and will cause the impurities to separate from the resulting solution and therefore be easily removable from the solution.

The mixing of the used oil 10 and the solvent mixture 14 causes the impurities to separate from the used oil and settle out as sediment rather than being held in suspension. Thus, in a vessel 18, a liquid phase having solvent mixture 14 and used oil 10 (minus the impurities) and a sediment phase having largely impurities with some solvent mixture 14 and used oil 10 are typically formed. The sediment phase is collected into a container 30 and the liquid phase is separated in a separator 46 and the recovered oil is collected into another container 34. The solvent mixture 14 from the separator 46 can be recycled back to vessel 18. As discussed, various processes such as distillation may be used to separate the solvent mixture 14 from the regenerated oil.

As discussed above, the used oil 10 will often contain significant amounts of water. Distillation may thus be advantageous to not only separate the solvent mixture 14 from the regenerated oil, but to separate water which has accumulated in the solvent mixture 14. The removal of the water from the solvent mixture 14 allows for reuse of the solvent mixture 14.

Turning now to FIG. 5, another process diagram of the present invention is shown. The diagram illustrates the basic process of FIGS. 1 and 4 and includes additional equipment, such as using a mixer 40 in the vessel 18. Slow mixing has been found to be advantageous as it may accelerate the separation of the impurities from the mixture of used oil 10 and solvent mixture 14. To increase the production rate, the system can have multiple separators, typically distillation columns 46A, 46B or the like.

The used oil 10 and solvent mixture 14 are mixed together. The mixture of chemical(s) and used oil are then introduced into a vessel 18. Slow mixing of the contents of the vessel 18 may be achieved by a mixer 40. Typically, a sediment layer and a liquid layer are formed. The liquid in the vessel 18 includes processed (regenerated) oil (used oil having the solid impurities separated therefrom), additives, water, and solvent mixture 14. Because of the volume of solvent mixture 14 necessary for processing the used oil 10, it is desirable to recover the solvent mixture from separators 46A and 46B and recycle it back into vessel 18 for processing additional used oil 10. The regenerated lubricant oil is collected in the container 34A and 34B.

The sediment containing the impurities may be withdrawn from the vessel 18. As the sediment will typically contain some liquid (oil and solvent mixture), it may be desirable to pass the sediment through a post-treatment unit such as a filter to separate any liquid from the impurities. The liquid is typically recycled back into vessel 18 and the impurities are collected in container 30.

In order to be environmentally friendly and economical, it is important to recover and recycle the solvent mixture. Thus, the amount of solvent mixture 14 remaining in the impurities and the oil and additives should be minimized.

Prior to processing as described in reference to the above figures, the used oil 10 was typically dark gray and opaque in appearance, likely due to the metal, carbon particles, and soot in the oil. After processing according to the above methods, the regenerated oil, which consisted of the oil and additives, was a lighter brown color and was transparent.

One advantage of the methods discussed above for separating impurities from used oil is the ability to perform the same without requiring elevated temperatures and pressures. The mixture of chemical(s) 14 will effectively separate the impurities from the used oil 10 at room temperature and pressure. It is appreciated that processes requiring elevated temperatures are generally more difficult and costly to construct and operate, while a system which can operate at atmospheric pressure and lower temperatures are simpler to construct and operate. These systems require less complex equipment, and typically require less energy.

The separation of solvent mixture 14 from the regenerated oil may be achieved using steam, heated water, electrical heating, or many other heat sources. The condensed solvent mixture recovered from the separators 46A, 46B will typically be at a temperature of about 50 degrees centigrade, and may be directly recycled into the system.

It will be appreciated that the temperature required for recovering oil from the used oil may depend somewhat on the composition and properties of the used oil, and the polar and non-polar solvents which are used.

There is thus disclosed an improved method for separating and recovering used oil. It will be appreciated that numerous changes may be made to the present invention without departing from the scope of the claims. 

1. A method for separating impurities from used oil comprising: selecting a used oil; selecting a polar solvent; selecting a non-polar solvent; mixing the used oil, polar solvent, and non-polar solvent; and separating solid impurities from the mixture of used oil polar solvent, and non-polar solvent.
 2. The method of claim 1, wherein the mixing step comprises mixing the polar solvent and non-polar solvent into a solvent mixture and thereafter mixing the solvent mixture with the used oil.
 3. The method of claim 2, wherein the mixing step comprises mixing the polar solvent and non-polar solvent to create a solvent mixture having between 5 and 15 percent non-polar solvent and the balance polar solvent.
 4. The method of claim 3, wherein the mixing step comprises mixing the polar solvent and non-polar solvent to create a solvent mixture having about 10 percent non-polar solvent and about 90 percent polar solvent.
 5. The method of claim 2, wherein the method comprises mixing the solvent mixture and used oil to create a mixture having between 15 and 50 percent used oil and between 50 and 85 percent solvent mixture.
 6. The method of claim 1, wherein the polar solvent is a ketone.
 7. The method of claim 1, wherein the polar solvent is acetone.
 8. The method of claim 1, wherein the non-polar solvent is an alkane.
 9. The method of claim 7, wherein the non-polar solvent is hexane.
 10. The method of claim 1, wherein the mixture of used oil, polar solvent, and non-polar solvent comprises between 2 and 13 percent non-polar solvent, between 42 and 81 percent polar solvent, and between 15 and 50 percent used oil.
 11. The method of claim 10, wherein the non-polar solvent is hexane and the polar solvent is acetone.
 12. A method for separating impurities from used oil comprising: selecting a polar solvent; selecting a non-polar solvent; mixing the polar solvent and non-polar solvent to form a solvent mixture; selecting a used oil having solid impurities therein; mixing the solvent mixture with the used oil to form a used oil mixture; and separating the solid impurities from the used oil mixture so as to form a processed oil mixture.
 13. The method of claim 12, wherein the method further comprises separating the solvent mixture from the processed oil mixture so as to recover the solvent mixture.
 14. The method of claim 13, wherein the method further comprises using the recovered solvent mixture to treat additional used oil.
 15. The method of claim 12, wherein the step of separating the solid impurities comprises allowing the impurities to settle out of the used oil mixture.
 16. The method of claim 12, wherein the step of separating the solid impurities comprises passing the used oil mixture through a filter.
 17. The method of claim 12, wherein the polar solvent is a ketone.
 18. The method of claim 12, wherein the non-polar solvent is an alkane.
 19. The method of claim 12, wherein the polar solvent is acetone and wherein the non-polar solvent is hexane. 